From twilight to pitch black, there are several factors that determine how dark an eclipse will be
Why? Despite “darkness in the day” being a common refrain when discussing total solar eclipses, it actually depends on the magnitude of the eclipse – how wide the path of totality is – and also where you stand to watch it.
1 – A very long totality, and so a very large moon shadow
2 – Observe close to the sunrise or sunset point at either end of the path of totality, and so stand under an elongated moon-shadow
3 – Watch from close to the Earth’s North or South Pole, which again means an elongated moon-shadow
4 – Any totality that’s blocked by lots of clouds and/or rain (it happens!)
Anyone watching the upcoming total solar eclipse in Chile or Argentina will be close to the end of the track. It will certainly be darker than in the USA last time out, though as Jörg pointed out to me, totality north of Rio Cuarto in Argentina will surely be very dark … check out how much land is covered by the elongated shadow:
In that example of the 2019 eclipse, the further you go east, the darker the totality will become … until it dips below the horizon southwest of Buenos Aires.
And the next eclipse? On December 14, 2020, there will be another total solar eclipse in South America, but it’s at lunchtime, and therefore midway through the path of totality. So as well as being only two minutes long, it won’t get very dark.
Pic credit: Pixbay (main image) & Xavier Jubier/Google Maps (inset image)